The bookmakers have heeded the warning: The odds on Manchester United achieving the quadruple plunged from around 20/1 last week to 14/1 on Sunday night in the wake of their demolition of Derby County and cruise through to the quarter-finals of the FA Cup.

The three-goal margin over a side struggling to stay in the Championship will not have instigated the plummet. More likely, it was the latest ominous demonstration of the depth, talent and versatility of the squad at Sir Alex Ferguson's disposal that will have persuaded the bookies to recognise that the quadruple - although, having lifted the Club World Cup in December, it should be said that United are actually chasing a Quintuple - is a realistic possibility.

Rather than highlight the quality of the players absent at Pride Park, it was the performances of Ryan Giggs and Cristiano Ronaldo in attack that served as the trenchant warning of the options available to Sir Alex. Presumably after a great deal of hard work on the training ground, the Manchester United manager has fostered an environment in which a ceaseless rotation of players and different combinations has seemingly become seamless.

Manchester United aren't just threatening to set new records this season. That would be too simple. What they're doing is contradicting established principles and proving that rotation can be implemented without any negative side-effects.

Since the start of the year, six different combinations have been used in attack and another half dozen in the centre of midfield and it is only opposing managers who are suffering for the uncertainty of who will be fielded. "It's impossible to prepare for playing against them. We watched them for six consecutive games and they played six completely different teams with different ways of playing. You can watch them in 60 consecutive ways but then they'll just change who plays where," complained Nigel Clough this weekend.

Preparation may not be an hot topic for debate when gossipers convene at the local pub but it matters. Consider the complaint of Juventus boss Claudio Ranieri last week in response to Luiz Felipe Scolari's exit: "We could have done without this change. Now the players will have an excuse and I, who had studied Scolari's team by memory, will have to start from the beginning. It will be another Chelsea and I will only have two weeks to get to know it."

Jose Mourinho famously - and presciently - named both teams the night before a Champions League tie between Chelsea and Barcelona two years ago; if he repeats the feat next Monday night then he will truly deserve to be regarded as special.

With so many players and so many options to choose from, Ferguson must be the envy of every manager in Europe. And nightmare. If the quadruple is achieved - and it is already all-but inconceivable United will finish the season with less than a treble - then it will be secured with Ferguson purposely defying a series of received wisdoms of modern-day management: no Makelele-type holding midfielder, no out-and-out front man even when Berbatov or Wayne Rooney are playing, and no apparent first-choice eleven.

And it is the impression that Ferguson is rotating without the anchor of an identifiable first-choice eleven that is perhaps the most remarkable aspect of United's relentless march. Ferguson's preference, this season at least, appears to be against having a preferred line-up in mind, ensuring his squad is permanently driven by internal rivalry - there will be no complacency shown on the training ground, that's for sure - and fresh legs are ready for future engagements. Therein is perhaps the clue to the reason why Manchester United seem so disconcertingly capable of achieving another unprecedented feat this season.

It is a great pity that Ferguson is so reluctant to talk to the press and so brusque whenever he agrees to an audience. Beneath that truculent, paranoid veneer is probably the sharpest mind in the football business. Perhaps it will be seen as a surprise that the Premier League's oldest dog is still experimenting with new tricks. But it ought not to be. Ferguson deftly follows football's tides closer than anyone else in the game and, just as constant evolution has been the theme of his 20-year tenure at Old Trafford, it is this dexterity which has underpinned his longevity.

Pete Gill